Yes, the "?" is a digit placeholder, like "0" but for spaces.
The "?/2400" is a format for displaying numbers as simple fractions, namely, as twenty-four-hundredths. Similarly, "?/2" is a format for displaying numbers as halves, etc.
Interesting. Is this documented somewhere? I couldn't find it.
I ran a few simple tests.
[TABLE="class: grid, width: 467"]
<tbody>[TR]
[TD="align: center"]R/C[/TD]
[TD="align: center"]C[/TD]
[TD="align: center"]D[/TD]
[TD="align: center"]E[/TD]
[TD="align: center"]F[/TD]
[TD="align: center"]G[/TD]
[TD="align: center"]H[/TD]
[TD="align: center"]I[/TD]
[TD="align: center"]J[/TD]
[TD="align: center"]K[/TD]
[TD="align: center"]L[/TD]
[/TR]
[TR]
[TD="align: center"]5[/TD]
[TD="align: center"]CF->[/TD]
[TD="align: center"]?/1[/TD]
[TD="align: center"]?/2[/TD]
[TD="align: center"]?/3[/TD]
[TD="align: center"]?/4[/TD]
[TD="align: center"]?/10[/TD]
[TD="align: center"]#/10[/TD]
[TD="align: center"]0/10[/TD]
[TD="align: center"]00/10[/TD]
[TD="align: center"]0.0/10[/TD]
[/TR]
[TR]
[TD="align: center"]6[/TD]
[TD="align: center"]1[/TD]
[TD="align: center"]1/1[/TD]
[TD="align: center"]2/2[/TD]
[TD="align: center"]3/3[/TD]
[TD="align: center"]4/4[/TD]
[TD="align: center"]10/10[/TD]
[TD="align: center"]10/10[/TD]
[TD="align: center"]10/10[/TD]
[TD="align: center"]10/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
[TR]
[TD="align: center"]7[/TD]
[TD="align: center"]2[/TD]
[TD="align: center"]2/1[/TD]
[TD="align: center"]4/2[/TD]
[TD="align: center"]6/3[/TD]
[TD="align: center"]8/4[/TD]
[TD="align: center"]20/10[/TD]
[TD="align: center"]20/10[/TD]
[TD="align: center"]20/10[/TD]
[TD="align: center"]20/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
[TR]
[TD="align: center"]8[/TD]
[TD="align: center"]3[/TD]
[TD="align: center"]3/1[/TD]
[TD="align: center"]6/2[/TD]
[TD="align: center"]9/3[/TD]
[TD="align: center"]12/4[/TD]
[TD="align: center"]30/10[/TD]
[TD="align: center"]30/10[/TD]
[TD="align: center"]30/10[/TD]
[TD="align: center"]30/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
[TR]
[TD="align: center"]9[/TD]
[TD="align: center"]1.5[/TD]
[TD="align: center"]2/1[/TD]
[TD="align: center"]3/2[/TD]
[TD="align: center"]5/3[/TD]
[TD="align: center"]6/4[/TD]
[TD="align: center"]15/10[/TD]
[TD="align: center"]15/10[/TD]
[TD="align: center"]15/10[/TD]
[TD="align: center"]15/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
[TR]
[TD="align: center"]10[/TD]
[TD="align: center"]0.1[/TD]
[TD="align: center"]0/1[/TD]
[TD="align: center"]0/2[/TD]
[TD="align: center"]0/3[/TD]
[TD="align: center"]0/4[/TD]
[TD="align: center"]1/10[/TD]
[TD="align: center"]1/10[/TD]
[TD="align: center"]1/10[/TD]
[TD="align: center"]01/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
[TR]
[TD="align: center"]11[/TD]
[TD="align: center"]0.2[/TD]
[TD="align: center"]0/1[/TD]
[TD="align: center"]0/2[/TD]
[TD="align: center"]1/3[/TD]
[TD="align: center"]1/4[/TD]
[TD="align: center"]2/10[/TD]
[TD="align: center"]2/10[/TD]
[TD="align: center"]2/10[/TD]
[TD="align: center"]02/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
[TR]
[TD="align: center"]12[/TD]
[TD="align: center"]0.25[/TD]
[TD="align: center"]0/1[/TD]
[TD="align: center"]1/2[/TD]
[TD="align: center"]1/3[/TD]
[TD="align: center"]1/4[/TD]
[TD="align: center"]3/10[/TD]
[TD="align: center"]3/10[/TD]
[TD="align: center"]3/10[/TD]
[TD="align: center"]03/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
[TR]
[TD="align: center"]13[/TD]
[TD="align: center"]0.5[/TD]
[TD="align: center"]1/1[/TD]
[TD="align: center"]1/2[/TD]
[TD="align: center"]2/3[/TD]
[TD="align: center"]2/4[/TD]
[TD="align: center"]5/10[/TD]
[TD="align: center"]5/10[/TD]
[TD="align: center"]5/10[/TD]
[TD="align: center"]05/10[/TD]
[TD="align: center"]error[/TD]
[/TR]
</tbody>[/TABLE]
A few observations:
- It appears that it rounds the number on the left (rather than truncating).
- The "#" and ")" codes also work (in addition to "?").
- No other formatting codes are allowed to the left of the "/".
So what is this good for? I can't imagine where I'd use it?